Traffic safety markings on roadways (lane stripes, crosswalk lines, turn arrows, words and the like) are made with a special traffic safety paint that is very tough, durable and brightly colored for high visibility (e.g., white, bright yellow, etc.). Traffic safety markings may also be applied to vertical surfaces, such as highway barrier walls. The nighttime headlight-reflecting capability of the traffic safety paint can be greatly enhanced by embedding small glass spheres (retroreflective beads) in the surface of the paint. In some cases it may be desirable to increase the surface roughness of the paint by embedding an anti-skid agent, e.g., sand, grit. The present invention relates particularly to devices and methods for embedding glass beads, anti-skid agents, and the like in traffic safety markings, particularly limited area markings that cannot be done by a vehicle-mounted sprayer moving along the roadway, as in lane striping. For example, crosswalk lines, turn arrows, and words like “STOP” are limited area markings. Nevertheless, it should become apparent that the invention is also applicable for non-limited area markings wherein the inventive device is mounted on a vehicle.
Reflective and anti-skid traffic safety markings are generally applied in two steps: paint application, and then bead (or anti-skid agent or other particulate) embedding. For lane striping vehicles, the two steps can be performed in quick succession by mounting a particulate spray head behind, i.e., trailing, a paint spray head.
For the sake of clear and focused description, the present disclosure is primarily focused on apparatus and related method for applying (embedding) retroreflective glass beads to wet paint, since this is the most problematic type of particulate to apply due to the characteristics of tiny glass beads. Given the present disclosure, it should be apparent to engineers of ordinary skill how to adapt the disclosed glass bead application apparatus and method embodiment(s) to be used for spraying other particulates, like sand for skid resistance, into paint like the traffic safety marking paint discussed herein.
The limited area safety marking is typically conducted as follows. For paint application, the area is preferably swept or blown clear of dust and debris, and then paint is hand sprayed or poured into stencils for non-linear area markings such as lettering and arrows. The paint is fast drying, and depending upon the type of paint, may be anywhere from about 10 mil to about 100 mil thick (1 mil=0.001 inches). For example, a quick-hardening material sold by the inventors' company includes a liquid pigmented paint and a powdered catalyst that are mixed on site for immediate use, since the mixture becomes totally hardened in about 20 minutes. The catalyzed mixture is poured into a stencil laid on the pavement, and is spread/leveled with a squeegee blade wide enough to span the stencil's openings. The paint layer resulting from such stenciling is generally about 100 mil thick (0.1 inches).
The reflective beads (or other particulates) are applied to the wet paint before it hardens. The beads can be scattered by hand like sowing grass seed, but preferably a hand-held spray gun wand drops (gravity fed) or shoots (air blown) beads down into the wet paint. Since hand-scattered application methods result in extremely uneven and wasteful bead distribution (glass beads are relatively expensive), the best bead application method is the air-blown method. Also, both gravity dropped and hand strewn beads do not impinge on the paint with sufficient force to embed the beads very deep. For good wear resistance, the beads must be embedded as deeply as possible while still leaving a portion exposed for light reflection. Having some beads more deeply embedded provides continued reflective properties even after the paint has been worn down enough to dislodge the top layer of beads.
Known prior art air-blown applicator equipment uses an air compressor to force beads out of an airtight hopper (“pot”) and through a hose to a nozzle that is typically small and round and therefore emits a relatively narrow, outward spreading, cone shaped spray of beads. The narrow cone yields a non-uniform bead and embedding force distribution as the spray nozzle is moved and tilted; furthermore the narrow application swath causes striations like corn rows when the nozzle must take several passes to cover a wide area. The bead pot is pressurized by an air compressor line, and the pot outlet goes into a flexible hose leading to the spray nozzle. For manual spraying, a hand held wand (rigid section of tubing) is employed between hose and nozzle to enable the user to control the nozzle position near the ground while standing.
There are a number of problems with the prior art air-blown devices.    1. Air compressors are heavy and bulky and thus are generally mounted on a wheeled carrier for limited area painting. They are also relatively expensive, and difficult to transport to a work site.    2. Air compressors compact ambient air which may be humid, thereby greatly increasing the amount of water contained in a stream of air output from the compressor. Sometimes the compressor may also leak lubricating oil into the output stream. Condensed water and/or oil vapor causes what is known as “packing” or clumping of the beads in the pot, periodically slowing or even stopping the flow of beads until the clumps can be broken up, and/or removed and thrown away (costing both time and money).    3. The prior art compressor driven devices and nozzles are known for producing striations, patchiness, uneven embedding depth, and other such non-uniformities of bead distribution in and on the paint, which translate into non-uniform light reflection and uneven wearing over time.    4. Prior art applicator hoses often suffer from a buildup of static electricity due to glass bead friction against the rubber/plastic hose interior. This can cause problems of static discharge shock to a user, and/or static electric effects on bead distribution.
Therefore it is an object of the present invention to address these problems to provide a relatively inexpensive and light weight bead (particulate) applicator that embeds the particulates in a painted surface with a maximum of uniformity and a minimum of waste and time/effort. Preferably these objectives are met not only for wheeled cart-type line stripers, but also in usage that requires hand holding of the applicator outlet.